High Lights of Modern Industrial Chemistry A symposium preeented before the Diviaion of Industrial and Engineering Chemistry a t the 86th Meeting of the American Chemical Society, Chicago, Ill, September 10 to 15, 1933.
Modern Solvent Industry E. W. REID, Mellon Institute of Industrial Research, Pittsburgh, Pa. accelerated by the introduction OR many year3 the solThe production and use of solvents hus become of nitrocellulose lacquers and vent industry was conione of the more important industries, both f r o m their rapid growth and wide use. p a r a t i v e l y small, and the standpoint of etolume production and general As the specifications of lacquers the p r o d u c t s w e r e of simple utility. During the past ten years new soluents became more rigid, new solvents structure and compcisition. The were demanded. 0 b v i o u s 1y have appeared ut a n approximate rate of twelae only solvents that were produced this one i n d u s t r y c o u l d not in q u a n t i t y were methyl and per year, and in 1932 their volume reached absorb a n indefinite quantity or ethyl alcohols, acetone, glycerol, 900,000,000 pounds, excluding the petroleum and number of new products. As a and the aromatic arid petroleum aromatic hydrocarbons. Solz!ents are used in result, new uses were developed h y d r o c a r b o n s . These prodpractically ez!eryY industry and contribute in some for new solvents, and, as thesc ucts were obtained from natural manner lo the necessities, luxuries: and arts of outlets were expanded, further sources, from fermentation, or investigations i n d i c a t e d inias by-products. the present day. T h e nitrocellulose lacquer inp r o v e m e n t s i n t h e products Investigation of the fermentadustry is probably the largest single user f o r solwhich often caused an additional tion methods r e s u l t e d in the vents. T h e new type solvents sometimes replace demand for a new type of solvent. production of acetone and butyl the older and better-known products of the indusAt the present time, solvents are alcohol from grain. T h i s try, but on the whole tend to contribute to the used in practically every industry process gave c o m p a r a t i v e l y and contribute in some manner cheap butyl alcohol that could general knowledge of the application of solvents to the necessities, luxuries, and be e s t e r i f i e d r e a d i l y to the which, in turn, contributes to the increased use arts of the present day. acetate, resultingin theinitiation of the older, products. of the modern l a c q u e r indusLACQUER INDUSTRY try, which, in turn, stimulated interest in the solvent field. Obviously the number of s01The nitrocellulose lacquer industry is one of the largest vents that could be produced by natural processes was users of solvents although i t is uncertain if this market can limited; consequently, as the demand for solvents of specific be considered a stable outlet, as the field penetrated by the properties became more urgent, it was necessary to resort to present type of lacquer is being invaded by the single-resin synthetic methods. type of finish. This type of coating may require special As a result, over one hundred solvents are produced on a solvents or mixtures of solvents of comparatively simple commercial scale at, the present time. Even the older prod- composition. Initially the lacquer formulator was limited ucts are being synthesized by new methods that are competi- in his choice of solvents but, a t the present time, there is a tive with the natural processes. This industry has grown solvent to meet practically any demand or requirement. with increasing rapidity during the past few years and in A lacquer solvent is more than merely a vehicle for trans1932 produced and sold approximately 900,000,000 pounds ferring a solid from one place to another in a convenient of solvents, excluding the petroleum and aromatic hydrocar- manner. It must not only be a good solvent for nitrocellubons. New methods of production hare lowered costs and lose but also for the resin used in the lacquer and should have created a highly competitive market in the more common the property of wetting pigments. Lacquer solrents are solvents. o;ten classified as low, medium, and high boilers. This classiEven the aromatic hydrocarbons that are by-products will, fication is not satisfactory since the rate of evaporation of a in the near future, be forced to compete with hydrogenated solvent from a lacquer film is of more importance than its petroleum naphthas that will undoubtedly be lower in cost boiling point. Alcohols evaporate more slowly than their and have similar solvent properties. corresponding esters of higher boiling points, and a nonsolAn economical method for the production of synthetic vent will leave a film more rapidly than a solvent. In addicamphor is an established fact, and it is extremely doubtful tion, the rate of evaporation of a single solvent is affected by if the natural product can compete under norni:il conditions. the presence of other solvents and ingredients. The informaThe modern solvent industry is comparatively new; con- tion available on the rate of evaporation of binary, ternary, sequently, with the exception of the solvents mentioned, and tertiary mixtures is very meager. Consequently, the practically all products of the industry may be classified as drying time of a lacquer, using a definite solvent mixture, new solvents. This applies purely to their conimercial pro- cannot accurately be determined except by actual test in the duction, as most of them have been known in the laboratory lacquer. The solvents that ha.i.e a slow rate of eT-aporation for many years. normally decrease the humidity blush of the lacquer film, The initial interest in the solvent field was stimulated and while those that evaporate rapidly increase this tendency.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Examination of vapor pressure curves of two solvents sometimes shows that these curves cross and that the real vapor pressure varies with the temperature, irrespective of boiling point. It is believed that this is caused by the molecules of one of the liquids being associated at normal temperatures and that this association causes a diminution of the vapor pressure of a substance but breaks down progressively as the temperature rises. This is specially noted among those solvents having a hydroxyl group such as the alcohols and acids; it is probable, for this reason, that the alcohols evaporate more slowly than their esters of higher boiling point. Not only may a single liquid form associated molecules but solvents, on mixing, often associate with each other. Solvents have also been classified as polar and nonpolar. The former class, comprising solvents like the alcohols and ketones that contain a hydroxyl or carbonyl group, have high dielectric constants and show strong polarity. The aromatic and petroleum hydrocarbons, carbon disulfide, and the like that are characterized by low dielectric constants are classed as nonpolar. The mixing of solvents quite often changes their individual solvent power. Several of the chlorinated compounds that are not solvents for the cellulose esters may, when mixed with an alcohol which is also a nonsolvent, become a good solvent. On the other hand, when a good solvent for cellulose esters is mixed with a petroleum or aromatic hydrocarbon, the solvent power is decreased. The hydrocarbons are low in cost, and it is the desire of the lacquer formulator to use as large a quantity of these diluents as possible. I n order to meet the demand of the modern lacquer industry for low-cost solvents and thinner mixtures, it has been necessary and desirable to use petroleum hydrocarbons as diluents. As a result, there are a t the present time a number of solvents of recent develop ment that have a comparatively high tolerance for petroleum hydrocarbons. The esters of the lactate type, especially butyl lactate and the butyl ether of ethylene glycol, were prepared to meet this demand. There are a large number of esters available to the lacquer industry, including the formates, acetates, phosphates, butyrates, stearates, and propionates. There is also the corresponding number of alcohols, including not only methyl, ethyl, and isopropyl, but also a secondary, iso, and tertiary butyl and amyl. Recently a hexyl and octyl alcohol have appeared on the market. While the esters are greater in number than any other type of solvent, they are not used in as many industries as the alcohols, ethers, or ether-alcohols. The ketones have also received considerable attention as lacquer solvents. In addition to acetone, there are being produced on a commercial scale, methyl ethyl, methyl propyl, methyl butyl, methyl isobutyl, methyl amyl, and dipropyl ketones. The ketones as a group are excellent solvents for nitrocellulose and, in some cases with the addition of an alcohol, are solvents for cellulose acetate. Recently, several of the solvent manufacturers have marketed mixtures of esters that were composed chiefly of the secondary and/or isoamyl acetates and propionates, to which has been added a small amount of ethyl acetate. The ether-alcohol type of solvent, such as the methyl, ethyl, and butyl ethers of ethylene and diethylene glycol, has a high solvent power for nitrocellulose and was developed to permit the formulation of odorless lacquers. I n addition to the solvents that evaporate rather rapidly from the lacquer film,there is a large number of very highboiling or plasticizing solvents. The most popular of these are the phthalates and phosphates, although recently the sebacates, sulfonamids, and oxidized or acetylated vegetable oils have received considerable attention. A new group of solvents is being introduced t o the lacquer industry that may
Vol. 26, No. 1
be considered as midway between high-boiling solvents and plasticizers. These are the esters of levulinic acid. While there is a large number of solvents for nitrocellulose covering practically any desirable rate of evaporation, there is a limited number for cellulose acetate. These are coniked to several of the methyl compounds, the lower ketones, the ketone alcohols, and the cyclic ethers such as the dioxanes. It is a notable fact that all the available aliphatic solvents for cellulose acetate are water-soluble while those for nitrocellulose may be soluble or insoluble in water. It has been erroneously stated that water-soluble solvents should not be used in the formulation of lacquers. It can be readily demonstrated that lacquers may be prepared from the water-soluble solvents equivalent in flow, gloss, and resistance to weathering and humidity blush to those prepared with the water-insoluble solvents, provided the solvent mixture is properly balanced. SURFACE-COATING FIELD The older methods of staining wood for finishing required the use of a water-soluble stain, which, on application, tended to raise the grain of the wood. The development of modern solvents has permitted the use of nonaqueous wood stains. Several of the higher boiling esters, and the glycols and their ethers appear not only to have the property of dissolving this type of dye, but also of giving good penetration into the wood and more even staining without raising the grain. Likewise the fast-drying types of varnish are improved in clarity, viscosity, and flow, and their drying time is decreased by the use of the hydroxy ether type of solvent. The viscosity and flow of dipping paints may be readily adjusted in the same manner.
TEXTILE INDUSTRY The development of the rayon industry, which is a large user of solvents, directed the attention of textile manufacturers to their use and application. As a result, the textile industry has become an important user of solvents in the conditioning of textile fibers and in the increasing of the efficiency of dyes. Certain types of dyes are soluble in furfural, the esters of the hydroxy acids, and the glycols and their ethers, and, when these solvents are used in the dye baths, less dye is required for a definite amount of cloth, and the color tone is improved. Several of the newer chlorinated solvents and cyclohexanol are used in scouring for the removal of paint and tar print marks from raw wool, and oil spots from cloth. They are also useful in fulling and scouring soaps where they eliminate hand-spotting, and in wetting-out agents and penetrants where they are compounded with soap and sulfonated oils or pine oil. Some of the new types of alcohols, such as cyclohexanol and diethylene glycol, are used as coupling agents in various textile oil compounds, in kier-boiling, and in peroxide bleaching of cotton to obtain better penetration by desizing. The solvent dissolves a portion of the natural wax, giving more thorough penetration of the bleach. The polyhydric alcohols and their ethers are also used in preparing various textile emulsions for the wool, cotton, silk, and rayon industries. They may act as a conditioning agent for the textile fibers or may increase the absorption of the oil by the fiber or act as a mutual solvent for the ingredients of the emulsion. They are especially valuable in basic dye baths, giving colors of better shades and more even leveling. The sulfonated or sulfated higher alcohols are used as wetting agents and detergents to an increasing extent. I n addition to their application to textiles they are suggested as general detergents in laundries and in scouring and cleaning
January, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
compounds for household purposes where they replace ordinary soaps.
use of a modern alcohol, or an alcohol-ether and hydroxy amine.
AUTOMOTIVE INDUSTRY
For many years the manufacturers of small metal parts used a solvent method for degreasing before finishing. Within the last few years, vapor-phase degreasing has been applied to larger units, including automobile bodies. The degreasing units are normally built to use low-boiling chlorinated solvents such as trichloroethylene, ethylene dichloride, and carbon tetrachloride, or mixtures of these and similar products. This method demands a solvent that shall be comparatively low-boiling, and of low fire and health hazard. I n addition to the use of solvents for cleaning and finishing, the automotive and aeronautical industries use solvents for removing carbon, as components of mixture in hydraulic brake and shock absorber liquids, and for high-temperature cooling. Ethyl alcohol was considered the standard automobile antifreeze for many years but, a t the present time, is forced to compete with methanol, glycerol, and ethylene glycol.
PETROLEUM INDUSTRY The petroleum industry has found that modern solvents may be a means of improving their products. Oils may be dewaxed with acetone, butyl alcohol, isopropyl ether, ethylene dichloride, or mixtures of these materials. I n the extraction method, dewaxing is carried out in a closed system and in a manner that will prevent an excessive loss of volatile solvent. It has been found economical and quite efficient. Recently there was announced a process for treating lubricating oils with dichloroethyl ether. This solvent was found to possess both the solvent power and the selectivity required in the extraction process for the manufacture of lubricating oil. By this method motor oils, equaling Pennsylvania grade in viscosity index and surpassing it in resistance to oxidation and sludging, are said to be produced from the Midcontinent, or Gulf Coastal and California oils. ,The pressurecarrying capacity of high-pressure greases and gear compounds is increased by the addition of a n oil-soluble, highboiling chlorinated solvent. The introfying action of the penetrating oils is due to the presence of chlorinated solvents.
PHARMACEUTICAL AND COSMETIC INDUSTRIES The pharmaceutical and cosmetic industries are rather large consumers of modern solvents. The extraction, separation, and purification of various plant and seed constituents and glandular extracts require the use of low-boiling stable materials. Several of the new ethers and chlorinated solvents have been found to have special merit for this purpose. Others of the polyhydric alcohol type are used to disperse or dissolve the active ingredient in a number of medicinal preparations. The extraction of some essential oils and medicinals requires an extractant that can be removed a t low temperature. The butanes, methyl chloride, and similar products are satisfactory for this purpose and, in addition, are used as refrigerants in household refrigerators. It is well known that the cosmetic industry is an important user of ethyl alcohol and glycerol, but it is not generally considered as a n outlet for solvents. A number of the new alcohols, ether-alcohols, and amines are being used to an increasing extent in this field. While most of these newer solvents are not essential to the preparation of cosmetics, they permit the formulation of products of exceptional merit. The better type of face and shaving creams are emulsions of a mineral, vegetable, or animal oil, and these emulsions may be stabilized and their emolient properties improved by the
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OTHERINDUSTRIES The improvement in leather finishes that has been so noticeable in the past few years is due to the use of the new type solvents that give even dyeing of the leather and a more uniform and brilliant finish. This is due to the introfying and leveling action of the solvent which carries the dye into the leather and prevents the color from rubbing off. This same penetrating action is obtained in regular printing inks, especially on paper that is highly sized and does not absorb the ink readily. The impregnation of paper fibers with wax and the conditioning of finished paper is improved by the use of some of the newer solvents, while certain household types of paper products may be given additional softness by treatment with a hygroscopic alcohol or amine. There are several of the newer solvents, such as cyclohexanol, the glycols, and glycol ethers, and the high-boiling amines, such as ethylene diamine, and triethanolamine, that may be classed as penetrants and introfiers. They are useful in a large number of products where impregnation is necessary and where the introfying effect is concerned with the carrying in of a dye or a solid material. For example, in the bleaching of straw hats it is essential that the bleach penetrate the straw thoroughly without decreasing its physical strength or harshening the fiber. These products are used in the impregnation of cloth and textile or other fibers with rubber latex solutions; in the same manner they increase the ease of impregnating such products as pump packings and hemp cables with greases and waxes. The food industry applies several of the new solvents to the fumigation of foodstuffs, to control fermentation in pickling vats, and to prevent putrefaction. The elimination of the dormant period of tubers, especially potatoes, resulting in a more rapid growth and increased yield, is accomplished by treating the tubers with dilute solutions or the vapors of the lower boiling chlorinated solvents or water-soluble chlorohydrins. The polyhydric alcohols and hydroxy amines are used to improve the qualities of glue binders used in composition cork and the like, and in book binding pastes to prevent curling and to increase the adhesive properties. The rate of reduction of silver nitrate in silvering solutions for silvering glass may be controlled by the use of these solvents, giving more even results and eliminating a large portion of defective pieces. The modern solvent industry is growing rapidly. During the past ten years there have been, on the average, twelve new solvents introduced each year. A number of these was formerly used in the essential oil industry where they commanded a high price but a t present are available in tank cars at low cost to the consumer. I n addition there is a large number of new solvents that are useful in a great variety of products and processes. It is obviously impossible to do more than indicate a few of the applications of these solvents, as they are used in some manner in practically every industry and in a number of ways in many. The new solvents replace a t times the older materials but, on the whole, increase the demand for them by contributing to a better knowledge of the use and means of using solvents. RECEIVED August 8, 1933.
GERMANEXPORTS OF NITROCELLULOSE LACQUERS INCREASE. Total exports of nitrocellulose lacquers from Germany advanced t o 5004 metric tons during the first 9 months of 1933 as against 4734 metric tons for the corresponding months of 1932. Principal countries of purchase were the Netherlands, France, Switzerland, Belgium, Sweden, and Italy.
